I think there's a simpler reason for this. The criticism that developers might just copy your software doesn't change for SaaS. Github doesn't need to be SaaS, it's just sold that way, and plenty of Github-clones have arisen.
I think there's a much simpler reason standalone software is a rare beast outside business and enterprise: piracy. It's an odd world where Oracle database can be freely downloaded but IntelliJ requires a license and a videogame requires Steam or an App Store or something. The broad pattern in standalone software is the more consumer-oriented the software, the more barriers to piracy there are in place.
The difference is that Oracle's customers are easier to sue. Oracle makes its money selling five-figure server licenses and piracy is no threat, even if the pirate gets some utility off the software. Heck, the pirate might eventually be forced to buy a license if he locks himself in. On the other side of the market, the piracy rates on consumer software are astronomical--as in 90% being a typical piracy rate that I've heard--and pirates go overwhelmingly unpunished. SaaS fixes the problem by ensuring the consumer never has a physical copy to steal.